Approximately 17 million people in the United States, or 6.2% of the population, have diabetes. Diabetes is a disease in which the body either does not produce or does not properly use insulin, a hormone that regulates blood glucose levels. The cause of diabetes is not known, although both genetics and environmental factors such as obesity and lack of exercise appear to play roles.
The two most common types of diabetes are type 1 diabetes and type 2 diabetes. Type 1 diabetes [formerly called insulin-dependent diabetes mellitus (IDDM) or juvenile-onset diabetes] develops when the body's immune system destroys pancreatic beta cells, the only cells in the body that make insulin. This form of diabetes usually strikes children and young adults, who require exogenous insulin to survive. It is estimated that 5–10% of Americans diagnosed with diabetes have type 1 diabetes.
Approximately 90–95% of Americans who are diagnosed with diabetes have type 2 diabetes [formerly called non-insulin-dependent diabetes mellitus (NIDDM) or adult-onset diabetes]. Type 2 diabetes usually begins as insulin resistance, a disorder in which the cells do not use insulin properly. As the need for insulin rises, the pancreas gradually loses its ability to produce insulin. Type 2 diabetes is associated with obesity, family history of diabetes, prior history of gestational diabetes, impaired glucose tolerance, physical inactivity, race/ethnicity, and older age.
Impaired glucose tolerance (IGT) and impaired fasting glucose (IFG) are considered to be prediabetic conditions. IGT is a condition in which the blood glucose level is elevated (between 140 and 199 mg/dL in a 2-hour oral glucose tolerance test), but is not high enough to be classified as diabetes. IFG is a condition in which the fasting blood glucose level is elevated (between 110 and 125 mg/dL after an overnight fast) but is not high enough to be classified as diabetes. Studies suggest that IGT and IFG may be reversible. With an increasingly aged population, however, IGT and development of type 2 diabetes are emerging as major worldwide public health problems. The cause of age-related impaired glucose tolerance remains to be defined.